What are these groups of ants doing? (Arkansas, US)

I live in Northwest Arkansas, United States. We have been observing an odd behavior - large black ants traveling in groups of maybe 12-24 individuals. They are in roaming "packs" rather than walking in narrow trails.

My best guess is that they are black carpenter ant workers - they are probably about 9 to 11 mm long, have very large heads and mandibles, and cream colored hairs on their abdomens. There is some difference in size and proportion within the packs - some have huge square heads, and some look more "normal."

So, are they patrolling for food? Trying to set up new colonies? (It has been an extremely rainy season and there is a lot of dead wood from an ice storm two or three years ago.) Something else? Why the loose, round packs rather than single-file lines?

The attached image is of one that a pack killed (or rather, tortured by two ants holding its middle legs and pulling them taut while others bit its head for several minutes, then dragged a foot to the side and left for dead). I assume that it was territorial behavior within the same species--do you think so? That is the only time I've observed an "execution" by a pack.

Would love to hear your expertise on the matter!

Hi!

Thanks for contacting us at AntAsk! We asked another ant expert, James Trager, for some help with this and here is what he had to say:

"The picture, sadly, does not help me. It looks vaguely like a mutillid or perhaps a Polyergus queen, rather than a conspecific of the pack-roaming ants as the writer suggests. The message strongly suggests Camponotus pennsylvanicus to me. They do sometimes recruit in (but usually linear) groups, but this roaming pack behavior sounds unusual, as the writer evidently recognized. I'd like to see it, and could probably interpret it better if so. If it were recruitment to a new nest site, I would expect them to be carrying brood, but there is no mention of that, so I can only guess that they are recruiting to a rich food source, such as a tree full of honeydew-secreting insects."

As James pointed out, it is impossible to tell what species of ant is in the picture as it is of poor quality. As he has mentioned, it could be a mutillid. Click here to find out more about these wasps that are sometimes mistaken for ants.

All the best,
James Trager (guest expert), Steffi Kautz & the AntAsk Team